1. Field of the Invention
The present invention is directed to the field of internal combustion engine ignition distributors and more specifically to an assembly for effectively interfacing a lightweight distributor rotor driveshaft formed of a material having a relatively high coefficient of thermal expansion with a rotational drive member having a relatively low coefficient of thermal expansion.
2. Description of the Prior Art
High voltage commutators for internal combustion engines are commonly called ignition distributors and normally include a base, which is attached to the engine and houses a shaft. The shaft is gear driven by the engine to rotate in synchronization with the engine. A rotor element is attached to the shaft inside a commutation cavity defined by the distributor base and a cap. The distributor cap is formed to mount on the base and contains several electrical contacts that are insulated from each other and connected to individual spark plugs of the engine. The rotor element may contain one or more commutation electrodes that provide electrical connection between the high energy voltage source electrode and individual ones of the spark plug contacts on the cap.
Traditionally, driveshafts, which connect between the engine synchronization gear and the rotor element inside the commutation cavity, were formed of metal in order to guarantee long life in severe temperature environments. Of course, since the driveshafts and the engine synchronization gear were generally formed of similar metallic materials having similar coefficients of thermal expansion, problems associated with interfacing between materials having dissimilar coefficients of thermal expansion was not evident. Conventional shafts and mounting techniques for distributors are shown in U.S. Pat. Nos. 4,011,476; 3,989,023; 3,799,135; 3,660,626; 3,646,922; and 3,258,551.
Although the conventional metallic rotor shafts are desirable in that they are easily lubricated and able to withstand the severe temperature variations of the automotive environment, they have the disadvantages of requiring highly accurate machining and careful assembly while at the same time, due to their mass, contribute a weight disadvantage to the associated vehicle.